1. Field of the Invention
The present invention relates to blade and ground speed controls in a self-propelled lawn cutting machine.
2. Description of the Related Art
Riding lawn mowers and similar lawn cutting machines conventionally include an engine which both propels the mower and powers the cutting blades. Both the blade speed and the ground speed of the mower are factors which may influence the quality of the resulting cut.
The primary factor determining grass cutting quality in a mower having a rotary blade is blade tip speed. As a general rule, higher blade tip speeds result in a higher quality cut. Safety considerations, however, place an upper limit on blade tip speeds and a blade tip speed of 19,000 feet/min. is generally considered the maximum desirable blade speed within the industry. The ground speed of the lawn mower may also have an impact on the quality of the cut.
In many conventional riding lawn mowers, the cutting blades are connected to the engine by flexible drive belts. In such a lawn mower, the blade speed is a function of the engine speed and belt slippage. The factors which relate the engine speed to the blade speed include the ratio of the engine pulley and the primary mower deck pulley.
Conventional riding lawn mowers also often include a mechanical governor for regulating the speed of the engine. The ground speed of the mower is typically controlled by the operator. If, during mowing operations, the vehicle is operated at an excessive ground speed, excessive clippings may collect in the mower deck inhibiting contact between the blades and the uncut grass resulting in such grass being folded over rather than properly cut. The quality of the cut may also be negatively impacted when the engine is placed under a heavier load and is unable to maintain the desired blade speed at the ground speed determined by the operator. For example, there may be situations where engine does not have sufficient power to maintain the desired blade speed when the mower encounters heavier grass without a reduction in ground speed.